I think your problem here is not so much that you don't know what RICO is, as that you don't have a tight grip on what the KKK is. It is probably the case that many, or even most, Klan members are also members of white supremacist criminal gangs. That those gangs are subject to RICO prosecution (a major Aryan gang was taken down that way just last year) illustrates the problem with your argument. The enterprise itself has to be focused on the racketeering-predicate crimes.